1. Field of the Invention
This invention relates to thrust bearings, and more particularly to a mechanism for proportionately distributing axial thrust loads between dual thrust bearing assemblies.
2. Description of the Prior Art
Thrust bearing assemblies function to prevent axial displacement of a rotating shaft by transmitting axial thrust loads generated in the shaft from the rotating inner ring of a bearing mounted on the rotating shaft through the bearing rolling elements to an outer ring secured to a stationary support member. For those applications where the shaft is subjected to bidirectional axial thrust loads, duplex rolling element bearings may be utilized to transmit the thrust loads, i.e., rolling element bearings are mounted in pairs such that the first rolling element bearing of each pair prevents axial displacement of the rotating shaft in a first axial direction while the second rolling element bearing of each pair prevents axial displacement of the rotating shaft in the other axial direction. Single-row radial bearings may also be used to support bidirectional axial thrust loads.
Under deep submergence conditions, such as experienced by the seawater pumps of deep diving submarines, the rotating pump shafts of the seawater pumps are subjected to increased axial thrust loads due to the increased hydrostatic pressure of the seawater. Due to the operating requirements of these types of pumps, the thrust bearing unit cooperating with the rotating pump shaft must be capable of transmitting these increased axial thrust loads in either axial direction.
One possible solution for handling the higher axial thrust loads experienced by rotating pump shafts subjected to deep submergence operating conditions is to increase the basic load rating of the rotating pump shaft's thrust bearing unit inasmuch as the basic load rating of a bearing is indicative of the axial thrust load the bearing is capable of handling. The basic load rating of a thrust bearing unit is dependent upon the bearing type, bearing geometry, number of rolling elements, contact angle, accuracy of fabrication and bearing material. The basic load rating of a thrust bearing unit may be increased by increasing the bore diameter of the bearing. Increasing the thrust bearing bore diameter, however, requires that the rotating pump shaft diameter be increased or redesigned to accommodate mounting of the thrust bearing unit. Moreover, increasing the thrust bearing bore diameter reduces the limiting rotational speed at which the bearing life becomes shortened.
Another alternative for increasing the basic load rating of a thrust bearing unit is to utilize a higher thrust bearing unit of a predetermined standard series. Although the bearing unit bore diameter remains constant, the bearing unit outside diameter, width and rolling element size are increased to accommodate the higher axial thrust loads. This larger thrust bearing unit results in increased weight, space and cost parameters which are negative considerations due to the space and weight constraints imposed in the design of pumps for deep diving submarines. Furthermore, thrust bearing units of a large size suitable for use in pumps in deep diving submarines are either not domestically manufactured or have not been acoustically qualified, i.e., rated to ensure that the maximum decibel level produced by the thrust bearing unit is less than or equal to a predetermined acceptable level.